Towing trailers using a vehicle is straightforward until it is necessary to reverse the vehicle. Operating in reverse a vehicle towing a trailer is a skill that must be learned. It is counter-intuitive because to turn the trailer to the left (when facing rearwardly) it is necessary first to turn the rear of the vehicle towing (or pushing in this case) the trailer to the right, which in turn means steering to the right to make the front of the vehicle move to the left. That is opposite to the direction of turning the steering wheel if the driver wanted to position the rear of the vehicle to the left in normal reversing without a trailer. Moreover, the direction of turn of the steering wheel soon needs to change, otherwise the trailer is apt to jack-knife with respect to the pushing vehicle. Because such reversing of a trailer is not frequently required, it is a skill that is not widely practiced, and therefore is not easily learned. It challenges many drivers and may even be a cause in some cases of a user choosing not to employ a vehicle with a trailer at all, but instead to acquire a larger vehicle that has the carrying capacity of a normal car and trailer without the need for a trailer.
Nevertheless, the technique for reversing a trailer is well understood and can be calculated and computed relatively easily when certain parameters are known, the most important being the geometry of the vehicle and trailer wheel bases. Indeed, the technology exists that can take over entirely the steering of a reversing trailer, provided the desired position and direction required of the trailer is known.
Tow-assist technology is known. There are two current options. A first provides a simple rear-facing camera and an in-cockpit screen on which the video image captured by the camera is displayed. When in tow-assist mode, and the vehicle is put into reverse gear (and knowing the geometry of the vehicle and the distance of the trailer axle from a towing hook), a computing system calculates the path a trailer will follow with a given (the current) steering input and displays it on the screen. The driver then needs to change the steering commands as the vehicle progresses in order to maintain a desired path. In this instance, for example, an initial right turn position of the steering wheel may be reflected by a left path for the trailer.
That may be as desired, but as the turn proceeds, if no change is made to the steering wheel, it is likely that the indicated path of the trailer will “tighten” rapidly. The driver needs to know that the steering must to be straightened to reduce the degree of turn of the trailer. The vehicle is at all times in the control of the driver.
The second option is to place into the video image the desired path to be taken by the trailer (for example by manipulating virtual tram lines in the image, or indeed by indicating an ultimate desired parking position in the image) and then leave the vehicle to steer itself appropriately under control of a computer algorithm, the driver merely operating the accelerator and brake and monitoring progress, releasing the steering wheel to be operated by the vehicle.
The latter system obviously involves positive power-assisted steering. That is, not merely amplification of steering movements implemented by the driver's actuation of a steering wheel, but initiation of steering movements under computer control. This is the first stage of steering-by-wire. However, complete steering-by-wire (that is, disconnection of a physical link between a steering wheel and the vehicle wheels to be steered) is not currently a practical arrangement (in the sense of being publicly or legally acceptable or permissible).
This system requires an interface between the driver and vehicle to input desired trailer trajectory, path or position instructions. In steering-by-wire, it would be feasible to use the vehicle steering wheel, because this could be disconnected from normal vehicle steering mode during trailer reversing. Aspects of the present invention provide such an arrangement. However, this is not going to be available unless and until steering-by-wire becomes a viable option in vehicles generally.
Nevertheless, whatever arrangement is provided for inputting commands for assisted reversing of a vehicle towing a trailer, it will always be a relatively rare occurrence to use those arrangements. Providing in-built controls for that purpose is somewhat excessive, particularly given the plethora of other controls already to be catered for; the “real estate” of a vehicle's dashboard and centre console (where control elements for a driver are typically located) is already crowded with functionality.
Some vehicle manufacturers have elected to use touch-screens and the like for both providing on-board information to the vehicle occupants as well as enabling input to the vehicle's control systems. Such screens work very well. However, other vehicle manufacturers employ more physical devices and indeed rotary knobs that are certainly better suited for some kinds of control than are touch screens. The reasons for this are multifarious and one advantage is the lack of necessity to watch the control while it is being operated. Steering control is one example where a rotary knob is potentially superior, since the driver can watch the surroundings while accurately inputting steering commands. Some rotary knobs are multi-modal. That is, they can operate different controls simply by selecting a particular function. This may be achieved by moving the position of the knob (e.g. axially) so that it engages different control elements of the knob. Alternatively, the knob may be universal having no endstops (that is, it may be rotated infinitely) and it is only a degree of rotation from a current position that is detected by the system it is operating, which may be switched between different functions by operation of other switches. The latter is not always desirable since there is no feedback that an end position has been reached.
It is an object of the present invention to provide a system that addresses the above issues and at least mitigates some of the problems discussed.